Remove XML step when generating rulesets

[legoktm]

The current workflow is:

• pull data from the SD directory API (JSON format) plus onboarded.txt (CSV)
• manually write an XML file for each instance (committed)
• parse the XML and concatenate all of them into a JSON blob (gitignored)
• compress the JSON and sign it (committed)

I think it would be easier to just write JSON files and lose the XML indirection. It made sense when we were still using HTTPSE's tooling, but that's no longer the case. We should just commit a pretty-printed JSON blob (either one per instance, or just one giant-but-not-really for everything) and the compressed + signed versions. That would also probably fix issues like #92.